Optical circuits include, but are not limited to, light sources, detectors and/or waveguides that provide such functions as splitting, coupling, combining, multiplexing, demultiplexing, and switching. Planar Lightwave Circuits (PLC's), also known as Planar Waveguides and Photonic Integrated Circuits (PICs), are a rapidly growing segment of the optical communications market, and will eventually subsume most of the optical technologies now in use for optical multiplexing, switching, amplification, etc. Planar lightwave circuits (PLCs) are optical circuits that are manufactured and operate in the plane of a wafer. PLC technology is advantageous because it can be used to form many different types of optical devices, such as array waveguide grating (AWG) filters, optical add/drop (de)multiplexers, optical switches, monolithic, as well as hybrid opto-electronic integrated devices. Such devices formed with optical fibers would typically be much larger or would not be feasible at all. Further, PLC structures may be mass produced on a silicon wafer.
Planar waveguides are tested by dicing a PLC wafer and mounting optical fibers to the edge of a PLC die. Light is sent in to the PLC structure through one optical fiber and a second optical fiber is used to detect the light. A photodetector coupled to the second optical probe detects the power of light transmitted to it. If the PLC works properly, then fibers are permanently attached to the PLC, and the PLC is put into a package. However, if the PLC does not work properly, then the unit is discarded, and the time, effort, and expense to dice, fiber mount, and comprehensively test the device are wasted. Also, in the near future, optical waveguides will appear as long distance (e.g., centimeters) signal carriers in high-speed electronics. There is also a growing body of technology based on surface plasmons.
Another challenge in testing these types of optical devices is to determine, in addition to the amount of light lost (escaped from the optical device) but also the specific location(s) in that device where light is being lost. Thus there is need for test equipment specifically designed test the performance of these various optical devices and to also provide specific information regarding the amount and location of light loss.